This research program is designed to investigate parameters which influence the subjective timing of the visual processing that precedes the subject's allocation of attentional capacity. The research primarily employs an experimental paradigm developed in this laboratory to reveal that processing of the semantic content of verbal stimuli and the structural parameters of spatial forms generates differences in the subjective duration of masked tachistoscopic presentations that do not permit stimulus recognition. The research is unique in indexing early visual processing without requiring, or even permitting, the subject to identify the presented stimulus.